Effects of cucurbit[n]uril (n = 7, 8, 10) hosts on the formation and stabilization of a naphthalenediimide (NDI) radical anion

Abstract

Most 1,4,5,8-naphthalenediimide (NDI) derivatives, especially those with mild π-acidity cannot achieve photoinduced electron-transfer (PET). Here we report our investigations on the binding interactions of a NDI diammonium dichloride salt (NDI·Cl₂) with cucurbit[n]uril (CB[n], n = 8, 10) and the formation process of a NDI radical anion upon photoexcitation of the NDI derivative in the presence of CB[n] (n = 8, 10). As a comparison, the influence of CB[7] on the PET process was also evaluated. The results show that the NDI core can be partially or fully encapsulated in CB[8] or CB[10] to form inclusion complexes at molar ratios of 1 : 1 (CB[8]·NDI²⁺) or 1 : 2 (CB[10]·2NDI²⁺). In the presence of the host, quick formation of the NDI radical anion was observed with respect to no radical anion formation without the host. According to the spectral results, interesting CB[8]-promoted charge-transfer interactions between the NDI radical anion and NDI²⁺ are assumed during UV irradiation. Moreover, from the UV/Vis and EPR spectra, the observation of intense signals of the NDI radical anion in the presence of CB[10], could presumably be related to a much better stabilized NDI radical anion encapsulated in CB[10].